This invention relates to a light-sensitive silver halide photographic material which has undergone a spectral sensitization, more particularly to a light-sensitive silver halide photographic material in which the spectral sensitivity in a red light-sensitive region is heightened, and the occurence of a photographic fog is restrained, and a storability with time is also improved.
With regard to the light-sensitive silver halide photographic material, there is now demanded the light-sensitive material having such photographic properties that the reproducibility of a color is not affected by a type of light source used at the time of a shot. It is considered to be suitable that a sensitizing maximum wave length of the light-sensitive layer sensitive to a red light region is set to the range of 620 to 650 nm and adjustment is made so that the spectral sensitivity in a wave length of 580 to 600 nm may be at least 40% of a maximum spectral sensitivity.
A technique of such a spectral sensitization, which is now suggested, comprises spectrally sensitizing a silver halide emulsion by the use of a combination of, for example, a benzothiazolecarbocyanine sensitizing dye and a benzimidazolecarbocyanine sensitizing dye or a benzimidazolothiacarbocyanine sensitizing dye. Such techniques disclosed in, for example, Japanese Patent Publications Nos. 6209/1974, 1569/1980 and 39460/1981; and Japanese Provisional Patent Publication No. 114419/1974, etc. However, the silver halide emulsion, which has undergone the spectral sensitization in the presence of the combination of such sensitizing dyes, is poor in the storability with time and has the drawback that a photographic fog is liable to occur during its storage, particularly at elevated temperature.
On the other hand, for the purpose of improving an image quality of the high-sensitivity light-sensitive silver halide photographic material (hereinafter referred simply to as the light-sensitive material), a variety of techniques has heretofore been developed. For example, one well known technique, by which image qualities such as gradation, graininess and sharpness are improved, comprises adding silver iodide to a silver halide composition, especially silver halide grains in order to utilize a development inhibition effect by virtue of iodine ions given off at the time of development.
For example, the silver halide emulsion used as the light-sensitive silver halide material for black-and-white photography generally contains 2 mole % or more of silver iodide, therefore this emulsion can be utilized in the above-mentioned technique with the intention of regulating the image qualities. Further, in particular, the light-sensitive silver halide material for color photography generally contains 4 mole % or more silver iodide. Thus the aforesaid technique can be utilized more effectively in the presence of this material. Such a high content of silver iodide is suitable for the improvement in the image qualities but it is not always preferred for the betterment of sensitivity, because the silver iodide acts to inhibit a sulfur sensitization reaction during a chemical ripening or a development reaction during a chemical ripening.
A desensitization resulting from the above inhibitive action at the chemical ripening or development can be fairly recovered, for example, by adding a greater amount of a sulfur sensitizer, a gold sensitizer or the like to the emulsion at the chemical ripening, but this disadvantageously deteriorates a stability with time of the emulsion solution, the light-sensitive material and the like.
Further, when the silver halide emulsion including silver iodide in great quantities is subjected to the spectral sensitization mentioned above, the photographic fog will occur very noticeably.
Accordingly, a first object of this invention is to provide a light-sensitive material which has a less photographic fog and a high red light sensitivity, when silver halide grains including silver iodide as a silver halide component are spectrally sensitized in a red light region.
A second object of this invention is to provide a light-sensitive material which has a less photographic fog and a high red light sensitivity, even after it has been stored at elevated temperature for a long period of time.